Structural, thermal, optical and dielectric properties of borosilicate glass composites containing tungsten, zinc and lithium oxides

The glass composites of composition, 0.45B2O3 + 0.15SiO2 + 0.05ZnO + (0.35 – x) WO3 +xLi2CO3; (0.25 ≤ x ≤ 0.34) were prepared by conventional melt quench technique and their non-crystallinity was confirmed XRD studies. Functional groups were extracted from FTIR and thermal properties were determined from DTA studies. The absorption spectra of glasses have been recorded in the wavelength range 400 nm to 800 nm. The optical band gap, Eg, (direct and indirect), Urbach energy (ΔE) and refractive index were determined. Dielectric properties were measured for the temperature range 303 K – 573 K and frequency range 100 Hz – 15 MHz. Dielectric constant and dielectric loss were found decreasing with frequency, increasing with temperature and increasing with Li2O concentration. The role played by Li2O and WO3 in the network modification leading to observed changes in glass transition temperature, optical band gap, dielectric parameters etc., has been discussed. Electric modulus has been analyzed and the nature of conducting phase of the glasses has been understood in terms of cole-cole plots. Relaxation time from both impedance and modulus were determined. Thermal activation of relaxation process was confirmed and its activation energy was determined. The power law behavior of ac conductivity has been established and frequency exponent was determined. Mott's small polaron hopping model fits gave the activation energy for dc and ac conductivity. The frequency exponent for ac conductivity decreased with increase of temperature which is as per the Correlated Barrier Hopping model’s prediction.